The invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to developer and toner compositions containing charge enhancing additives, which impart or assist in imparting a negative charge to the toner particles, and enable toners with rapid triboelectric charging characteristics, and excellent admix characteristics. In embodiments, there are provided in accordance with the present invention toner compositions comprised of toner resins, color pigment particles or dyes, and certain aluminum complex charge enhancing additives. In embodiments of the present invention, the charge additives are anionic aluminum complexes comprised of an anion of a central aluminum atom bonded to four ligands, and a counter cation of a proton, an alkaline metal ion, ammonium ion, or the like. In a specific embodiment of the present invention, the anion of the aluminum complex charge enhancing additive contains four identical ligands derived preferably from ortho-hydroxyphenols. The charge enhancing aluminum complexes of the present invention can generally be prepared by treating a mixture of an aqueous aluminum ion solution and two molar equivalents of an ortho-hydroxyphenol with two molar equivalents of a base, such as potassium hydroxide, sodium hydroxide, or an amine, followed by reacting the resulting intermediate with two molar equivalents of a phenol and a base. For the aluminum charge enhancing complexes with four identical ligands derived from ortho-hydroxyphenols, the synthesis involves simple treatment of an aqueous aluminum ion solution and four molar equivalents of ortho-hydroxyphenol with four molar equivalents of an appropriate base. The aforementioned charge additives in embodiments of the present invention enable, for example, toners with rapid triboelectric charging characteristics, extended developer life, stable triboelectrical properties irrespective of changes in environmental conditions, and high image print quality with substantially no background deposits. Also, the aforementioned toner compositions usually contain a colorant component comprised of, for example, carbon black, magnetites, or mixtures thereof, pigment particles like color pigments or dyes with cyan, magenta, yellow, blue, green, red, brown, or mixtures thereof thereby providing for the development and generation of black and/or colored images. The toner and developer compositions of the present invention can be selected for electrophotographic, especially xerographic, imaging and printing processes, including color processes.
Toners with negative charge additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064, the disclosures of which are totally incorporated herein by reference. The '974 patent discloses negatively charged toner compositions comprised of resins, pigment particles, and as a charge enhancing additive ortho-halophenyl carboxylic acids. Similarly, there are disclosed in the '064 patent toner compositions with chromium, cobalt, and nickel complexes of salicylic acid as negative charge enhancing additives. In U.S. Pat. No. 4,845,003, there are illustrated negatively charged toners with certain aluminum salt charge additives. More specifically, this patent discloses as charge additives aluminum complexes comprised of two or three hydroxybenzoic acid ligands bonded to a central aluminum ion. While these charge additives may have the capability of imparting negative triboelectric charge to toner particles, they are generally not as efficient in promoting the rate of triboelectric charging of toner particles. A fast rate of triboelectric charging is particularly important for high speed xerographic machines since, for example, these machines consume toner rapidly, and fresh toner has to be constantly added. The added uncharged toners, therefore, must charge up to their equilibruim triboelectric charge level rapidly to ensure no interruption in the xerographic imaging or printing operation. Another disadvantage of these charge additives is their thermal instability, that is they often break down during the thermal extrusion process of the toner manufacturing cycle. Additionally, the hydroxybenzoic acid ligands, particularly 3,5-di-tert-butylsalicylic acid, are expensive precursors for these additives. Most or many of these and other disadvantages are eliminated, or substantially eliminated with the metal complex charge additives of the present invention.
Developer compositions with charge enhancing additives, which impart a positive charge to the toner particles, are also well known. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions; U.S. Pat. No. 4,221,856 which discloses electrophotographic toners containing resin compatible quaternary ammonium compounds in which at least two R radicals are hydrocarbons having from 8 to about 22 carbon atoms, and each other R is a hydrogen or hydrocarbon radical with from 1 to about 8 carbon atoms, and A is an anion, for example sulfate, sulfonate, nitrate, borate, chlorate, and the halogens such as iodide, chloride and bromide, reference the Abstract of the Disclosure and column 3; a similar teaching is presented in U.S. Pat. No. 4,312,933 which is a division of U.S. Pat. No. 4,291,111; similar teachings are presented in U.S. Pat. No. 4,291,112 wherein A is an anion including, for example, sulfate, sulfonate, nitrate, borate, chlorate, and the halogens; U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, discloses developer compositions containing as charge enhancing additives organic sulfate and sulfonates, which additives can impart a positive charge to the toner composition; and U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, discloses positively charged toner compositions with resins and pigment particles, and as charge enhancing additives alkyl pyridinium compounds.
Illustrated in U.S. Pat. No. 5,275,900 are toner compositions comprised of polymer resins, colorants comprised of color pigment particles or dye molecules, and certain metal complex charge additives derived from the reaction of a mixture of a hydroxybenzoic acid and a base with a metal ion in the presence of an excess of a hydroxyphenol. More specifically, this patent illustrates a negatively charged toner composition comprised of polymer, colorant, optional surface additives, and a metal complex charge enhancing additive of the following formula ##STR1## where M is a metal; N+ is a cation; R and R' are alkyl, alkoxy, aryloxy, halogen, carbonyl, amino, nitro, or mixtures thereof; m and n are the number of R substituents ranging from 0 to 3; y- is the magnitude of the negative charge of the anion; and y' represents the number of cations.
Illustrated in U.S. Pat. No. 5,300,387 is a negatively charged toner composition comprised of a polymer or polymers, pigment, and a metal complex charge enhancing additive as essentially represented by the following formula ##STR2## where M is the central metal ion; N+ is the counter cation; R and R' are selected from the group consisting of alkyl, alkoxy, aryloxy, halogen, carbonyl group, alkoxycarbonyl group, amino group, nitro group or mixtures thereof; m and n are the number of R substituents on the aromatic rings, ranging from 0 to 3; y- is the magnitude of the negative charge of the anion or the number of the counter cations of the metal complex, and represents the number 1 or 2; and y' represents the number of counter cations N+.
In another U.S. Pat. No. 5,238,768, toner compositions containing novel bis(hydroxyaryl) sulfone charge enhancing additives are disclosed.
Also, there is illustrated in U.S. Pat. No. 5,250,380 a negatively charged toner composition comprised of resin, pigment, and an aluminum charge enhancing additive of the following formula ##STR3##
U.S. Pat. No. 5,250,379 a negatively charged toner composition comprised of resin, pigment, and an aluminum charge enhancing additive of the following formula ##STR4## and copending application U.S. Ser. No. 964,544 a toner composition comprised of a polymer or polymers, pigment particles and/or dyes, optional surface additives, and a charge enhancing additive of the following formula ##STR5## wherein R is hydrogen, alkyl, or aryl; R' and R" are selected from the group consisting of alkyl, alkoxy, aryl, and aryloxy; R'" is selected from the group consisting of alkyl, alkoxy, oxide, and halide; M is boron or a metal; x is a number of from 1 to 4; and y is a number of from 0 to 2.
The disclosures of each of the copending applications are totally incorporated herein by reference.
Although many charge enhancing additives are known, there continues to be a need for charge enhancing additives which when selected for toners, render toners with many of the advantages illustrated herein. There is also a need for negative charge enhancing additives which are useful for incorporation into black and colored toner compositions which can be utilized for developing positive electrostatic latent images. Moreover, there is a need for colored toner compositions containing charge enhancing additives which do not interfere with the color quality of the colorants present in the toners. Another need relates to the provision of toner compositions with certain charge enhancing additives, which toners in embodiments thereof possess substantially stable triboelectric charge levels, and display acceptable rates of triboelectric charging characteristics. Furthermore, there is also a need for toner compositions with certain charge enhancing additives which possess excellent dispersibility characteristics in toner resins, and can, therefore, form stable dispersions in toner compositions. There is also a need for negatively charged black and colored toner compositions that are useful for incorporation into various imaging processes, inclusive of color xerography, as illustrated in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference; laser printers; and additionally a need for toner compositions useful in imaging apparatuses having incorporated therein layered photoresponsive imaging members, such as the members illustrated in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Also, there is a need for negatively charged toner compositions which have desirable triboelectric charge levels of, for example, from between about -10 to about -40 microcoulombs per gram, and triboelectric charging rates of less than about 120 seconds, and preferably less than 60 seconds, such as 30 seconds or less as measured by standard charge spectrograph methods when the toners are frictionally charged against suitable carrier particles via conventional roll milling techniques. There is also a need for nontoxic, substantially nontoxic, or environmentally compatible charge enhancing additives which when selected at effective concentrations of, for example, less than 7 weight percent, preferably less than 4 weight percent, render the resulting toners environmentally acceptable. An additional need resides in the provision of simple and cost-effective preparative processes for the charge enhancing additives of the present invention. The concentrations of the charge additives that can be present generally range from about 0.05 weight percent to about 5 weight percent, depending on whether the charge additive is utilized as a surface additive or as a dispersion in the bulk of the toner. The effective concentrations of toner in the developer, that is toner and carrier particles, are, for example, from about 0.5 to about 5 weight percent, and preferably from about 1 to about 3 weight percent.